This invention relates generally to Diagnostic Imaging (DI) measurements, and, more particularly, to Bone Mineral Density (BMD) measurements which are the measurements of the amount of bone mineral per unit volume of bone tissue.
The accurate measurement of bone density with Computed Tomography (CT) requires a BMD reference phantom (generally solid Calcium Hydroxyapatite) to be scanned along with the patient scan such that the phantom appears in all the desired patient images. This is required since CT number values for human tissue (especially bone) change as a function of the size of the patient section and the amount of bone, fat, muscle, etc in the scan section. The reference phantom's CT values are affected similarly by the patient's characteristics. Thus, changes in the reference phantom values can be used to calibrate CT number readings from the patient's bone in order to calculate a more accurate BMD value. This is often done using commercial software products such as the QCT-3000 System commercially available from Image Analysis, Inc. of Columbia, Ky.
Most patient CT scans are prescribed for reasons other then BMD screening. It would however be useful to identify patients who are at risk for osteoporosis for follow-up study using information from a routine CT scan (i.e., not a specifically prescribed BMD scan). Specifically, this would require that a BMD estimate could be made with reasonable first order accuracy from bone Region Of Interest (ROI) measurements without the use of a BMD reference phantom.